Hollow waveguide discharge switching device having a capillary tube extending through the electrodes



Sept. 21, 1965 G. I. KLEIN 3,208,012

HOLLOW WAVEGUIDE DISCHARGE SWITCHING DEVICE HAVING A CAPILLARY TUBE EXTENDING THROUGH THE ELECTRODES Filed Feb. 28, 1962 WITNESSES 'NVENTOR fi MAQ, Gerald I. Klein.

ATTORNEY United States Patent of Penns lvania l iled Feb. 28, 1962, Ser. No. 176,333 5 Claims. (Cl. 333-13) This invention relates, in general, to discharge devices and, more particularly, to gaseous discharge ultra high frequency or microwave switching devices more commonly known a transmit-receive or T-R sw1tc hes.

T-R switches have been widely used in radar circuits to prevent a sensitive receiver of ultra short-wave signals, for example, 3,000 megacycles, to be operatively connected to the same antenna of a radar set to which a transmitter is connected. The T -R switch functions to short circuit the receiver the moment a pulse from the transmitter is transmitted to the common antenna and thus prevent an influx of power into the receiver, from the transmitter, which could damage the sensitive receiver.

To effect the above purpose, a T-R switch must change with great rapidity from a nearly non-conductive state to a conductive state when the transmitter pulse wave front appears, and must change back again to the nonconductive condition with great rapidity when the transmitted pulse has terminated. To effect this change, it is necessary that the gaseous medium of the switch shall rapidly ionize so that a space discharge may be initiated by a relatively small voltage rise, i.e., it should have a comparatively low break-down voltage, and it should deionize rapidly when the voltage is removed so that the return signal may be admitted to the receiver.

T-R switches having a pair of spaced electrodes with an ionizable medium such as argon and small amounts of water vapor within the electrode gap are known. While these switches generally operate at comparatively low firing powers, their recovery time is comparatively long. T-R tubes using an ionizable medium having a fast recovery time, for example, chlorine are also known. These switches comprise generally a quantity of chlorine which is enclosed in a quartz capsule. A resonant microwave aperture or iris is located on one exterior wall of the capsule. With the incidence of a high power level electromagnetic wave, a very high voltage occurs between the opposite edges of the iris causing ionization of the gas within the capsule. This ionized gas forms a low resistance path between the opposite edges of the iris through which the discharge is established and which, in turn, elfectively short circuits the path across the iris causing reflection of incident radiation. Switches of this latter nature have been found to have excellent properties at power levels above 100 watts peak with typical iris geometries employed in broadband switches. While such switches provide fast recovery times, in the order of 0.08 microsecond at approximately 1 kilowatt peak power, they do not operate below 50 watts peak. The inclusion of electrodes in the ioniza'ble medium having a fast recovery time, such as chlorine, would serve to reduce the power level at which the discharge occurs. However, known fast recovery gases are extremely detrimental to the material of the electrode and cause the corrosion of these electrodes, particularly during the discharge period.

Accordingly, it is an object of this invention to provide an improved electron discharge device.

A further object is to provide a microwave switching device having a low firing power level and a fast recovery time.

Another object is to provide a microwave switching device having extremely long life.

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Still another object is to provide a microwave switching device which is easily and economically manufactured.

Briefly, this invention accomplishes the above cited objects by providing a discharge device of the T-R switch type which includes a section of hollow waveguide open at both ends. A pair of electrodes are disposed within the waveguide and define a discharge gap into which is placed a capillary tube containing a readily ionizable medium having a fast recovery time. The incidence of radio frequency energy creates a strong electric field between the two electrodes, in the discharge gap, with the result that an arc discharge occurs within the ionizable medium contained within the capillary tube. By this arrangement, the benefit of both the electrode type switch and those of the fast recovery medium are achieved in a single device.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention, reference may be had to the accompanying drawing which shows in perspective partially broken away and partially in section, a microwave switching device embodying the present invention. Referring in detail to the drawing, there is shown a switch device incorporating the present invention in its preferred form. The device includes a section of hollow rectangular waveguide 10 having an upper wall 12, a lower wall 14, and two side walls 16. The waveguide section 10 is of a suitably electrically conducting material such as copper as is standard in the art. A pair of plate members 18 extend from each of the side walls 16 and are positioned in a plane which is substantially perpendicular to the major or longitudinal axis of the waveguide section 10. The plates 18 are of electrically conducting material such as copper and form the inductive part of a resonant circuit.

The capacitive portion of the circuit is defined by two electrodes 20 and 2-2 which extend towards the center of the waveguide section 10 from, respectively, the upper and lower walls 12 and 14. The two electrodes 20 and 22 are shown to be in the form of truncated cones and are of a suitable electrically conductive material such as copper. The cones 20 and 22 do not contact one another, but are spaced apart to define a discharge gap therebetween. The switch as thus far described is basically that of prior art devices incorporating the capacitive cone structure defining a discharge gap and inductive metallic members as is illustrated in the text, Micro- Wave Duplexers, by L. D. Sm-ullin and C. G. Montogomery, McGraw-Hill Book Co., Incorporated, New York, 1948, pages 67 to L12. The fundamental distinc tion existing between the art described in the above cited text and that of the present example is that those of the former are enclosed structures containing an ionizable medium While the device of the present example has both ends of the waveguide section 10 remaining open.

The various dimensions, spacing, etc., of the above described structure are determined by the various param eters of the system in which the device is to be utilized in a manner well known in the art. The system frequency is of particular importance.

The upper electrode 20 is provided with a centrally extending bore 24 which is in alignment with an aperture 21 in the upper wall 12 of the waveguide section 10. The lower electrode 22 is also provided with a bore 26 which extends for a portion of its length. A capillary or very small diameter tube 28 is disposed within the bores 24 and 26 and extends across the discharge gap defined by the electrodes 20 and 22. The capillary tube 28 is of a material capable of withstanding very high temperatures and having a low dielectric constant and low dielectric loss, for example, quartz. The capillary tube -28 is filled with a readily ionizable medium which has a fast recovery time for example, chlorine, chlorine admixed with small amounts of argon, or sulfur hexaflouride. The medium is at a pressure in the range of from 1 to 30 millimeters of mercury and typically in the range of about 5 to millimeters of mercury. In the preferred embodiment, the capillary tube 28 extends through the top wall 12 of the waveguide section 10 and is attached in fluid communication to a bulbous reservoir 30 which may also be of quartz. The reservoir 30 serves to increase the total volume of ionizable medium available to the capillary tube 28 and hence increase the useful life of the device.

The capillary tube 28 is relatively small and preferably has an inside diameter in the range of about 0.1 to 0.005 inch. The wall thickness of the capillary tube 28 is in the range of about 0.003 to 0.030 inch.

In operation, radio frequency energy incident upon the resonant circuit creates a high electrical field between the electrodes and 22. This high electrical field creates a discharge between these two electrodes; which discharge takes the path of least resistance. In this case, the path of least resistance is through the ionizable medium within the capillary tube 28. Because of the relatively close spacing of the electrodes 20 and 22, and because of the readily ionizable medium within the capillary tube 28 a low firing power or power to initiate discharge is required. Moreover, the small volume of gas which is disposed in the radio frequency field can be ionized to plasma resonance density by a very small amount of absorbed radio frequency power, thus reducing arc loss. Also, because the amount of quartz in the radio frequency field is very small, the amount of loss occasioned by its presence is likewise very small.

One particular model built in accordance with the present invention was found to operate over the power range of from 2 to 60 watts and had a recovery time of less than 0.1 microsecond. This particular device was also life'tested for 1 800 hours wit-h no appreciable change in its operating characteristics. Thus, it is seen there has been described a microwave switching device which is operable for low firing powers and which has a very fast recovery time and which, in addition, is easily and economically manufactured.

While there have been shown and described what is at present considered to be the preferred embodiment of the invention, modifications thereto will readily occur to those skilled in the art. For example, it is possible that in certain instances the inductive plates may not be absolutely necessary to the operation of the device and that these elements may be omitted therefrom. It is also possible that other than rectangular waveguides may be utilized in particular circumstances.

I claim as my invention:

1. A microwave switching device comprising a section of hollow waveguide, a pair of electrodes disposed within said waveguide in a first gaseous medium, said electrodes defining a discharge gap therebetween, each of said electrodes having a bore, an electrodeless tube positioned within said bores and extending across said discharge gap, said tube having an inside diameter of less than A of an inch, and a wall thickness of .003 to .030 inch, said tube containing a second gaseous medium which provides when ionized by radio frequency energy between said electrodes the path of least resistance between said electrodes, said first gaseous medium being less ionizable than said second ionizable medium.

2. A microwave switching device comprising a section of hollow waveguide, a pair of electrodes disposed within said waveguide and within a first gaseous medium, said electrodes defining a discharge gap therebetween, each of said electrodes having a bore located therein, an electrodeless capillary tube positioned within said bores and extending across said discharge gap, a reservoir means external to said discharge gap and in fluid communication with said capillary tube, said reservoir and said tube containing chlorine which provides when ionized by radio frequency energy between said electrodes the path of least resistance between said electrodes, said first gaseous medium being less ionizable than said second gaseous medium.

3. A microwave switching device comprising a section of hollow waveguide, a pair of electrodes disposed within said waveguide within a first gaseous medium and defining a discharge gap therebetween, each of said electrodes having a bore located therein, an electrodeless capillary tube positioned within said bores and extending across said discharge gap, a reservoir external to said discharge gap and in fluid communication with said capillary tube, said reservoir and said tube containing a second gaseous medium which is more ionizable than said first gaseous medium, said second gaseous medium providing when ionized by radio frequency energy between said electrode the path of least resistance between said electrode.

4. A microwave switching device comprising a section of hollow waveguide open at both ends and having an upper wall, a lower wall and two side walls, a pair of electrically conductive paths extending from each of said side walls in a plane substantially perpendicular to the longitudinal axis of said waveguide, first and second electrodes extending respectively from said top and bottom Walls and defining a discharge gap therebetween, said first electrode having a centrally located bore extending through the length thereof, said second electrode having a centrally located bore extending thereinto, said bores being in alignment, an aperture within said top waveguide wall in alignment with said bores, an electrodeless capillary tube disposed within said bores and across said discharge gap, said tube extending through said aperture to the exterior of said waveguide, and reservoir means exteriorly positioned with respect to said waveguide and connected to said tube, said reservoir and said tube comprising a hermetically sealed system and containing an ionizable medium therein.

5. A microwave switching device comprising a section of hollow waveguide open at both ends and having an upper wall, a lower wall and two side walls, a pair of electrically conductive plates extending from each of said side walls in a plane substantially perpendicular to the longitudinal axis of said waveguide, first and second electrodes extending respectively from said top and bottom walls and defining a discharge gap therebetween, said first electrode having a centrally located bore extending through the length thereof, said second electrode having a centrally located bore extending thereinto, said bores being in alignment, an aperture with said top waveguide wall in alignment with said bores, an electrodeless capillary tube disposed within said bores and across said discharge gap, said tube extending through said aperture to the exterior of said waveguide, and reservoir means exteriorly positioned with respect to said waveguide and connected to said tube, said reservoir and said tube comprising a hermetically sealed system and containing an ionizable medium therein, said ionizable medium including chlorine.

References Cited by the Examiner UNITED STATES PATENTS 2,594,732 4/52 Cork 33313 X 2,745,072 5/56 Goldstein et al. 2,776,409 1/57 Goldstein 3 3 3-13 FOREIGN PATENTS 722,406 11/ 51 Great Britain.

HERMAN KARL SAALBACI-I, Primary Examiner.

CHESTER L. JUSTUS, Examiner. 

1. A MICROWAVE SWITCHING DEVICE COMPRISING A SECTION OF HOLLOW WAVEGUIDE, A PAIR OF ELECTRODES DISPOSED WITHIN SAID WAVEGUIDE IN A FIRST GASEOUS MEDIUM, SAID ELECTRODES DEFINING A DISCHARGE GAP THEREBETWEEN, EACH OF SAID ELECTRODES HAVING A BORE, AN ELECTRODES TUBE POSITIONED WITHIN SAID BORES AND EXTENDING ACROS SAID DISCHARGE GAP, SAID TUBE HAVING AN INSIDE DIAMETER OF LESS THAN 1/10 OF AN INCH, AND A WALL THICKNESS OF .003 TO .030 INCH, SAID TUBE CONTAINING A SECOND GASEOUS MEDIUM WHICH PROVIDES WHEN IONIZED BY RADIO FREQUENCY ENERGY BETWEEN SAID ELECTRODES THE PATH OF LEAST RESISTANCE BETWEEN SAID ELECTRODES, SAID FIRST GASEOUS MEDIUM BEING LESS IONIZABLE THAN SAID SECOND IONIZABLE MEDIUM. 